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There are no data available in the literature that have specifically evaluated differences in adaptation to unilateral conductive or sensory changes. However, based on clinical experience it may be postulated that changes of outer or middle ear function appear to be tolerated more easily than those of cochlear origin. Very often, patients seen in the clinic are unaware of a slight conductive hearing loss. By contrast, patients are immediately disturbed by a minor decline of cochlear function. One of several complaints of these patients is a change in their spatial orientation or difficulties in understanding speech in a noisy environment . The goal of the study was to determine if binaural performance tested psychoacoustically using a lateralization task is influenced differentially by short-term induced unilateral conductive or sensory changes. Lateralization performance was evaluated in seven normal-hearing subjects during induced auditory periphery asymmetry resulting from: l. exposure to noise presented for 5 minutes at 115 dBA SPL or 2. bilateral occlusion with earplugs of unequal attenuation for 48 hrs. An adaptive procedure was used to detenmine hearing thresholds of a 4-kHz narrow-band noise (NBN). In a lateralization task subjects indicated the positions of intracranial images created by the same NBN pr esented binaurally at SO dB SL with interau ral level differences ( I LDs) varying within plus/minus 12 dB. The tests were performed over a one-hour period post-exposure, immediately prior to and following plugging the ears, and at 24 and 48 hrs post-plugging. Immediately after the exposure or after plugging, there was a shift of lateral ization towards an unexposed side or the side blocked by the plug with a smaller attenuation, respectively. After a few minutes post-exposure, signals with I LD=0 were lateralized at midl ine. Within 30 minutes post -plugging, those signals were gradually lateralized closer to midline but remained off center for the rest of the plugging period. Thus, subjects showed fast adaptation to induced unilateral sensorineural changes and incomplete adaptation to induced asymmetrical conductive changes. Those rather unexpected r esults can be explained using a qualitative model assuming that: 1. a conductive impainment reflects a loss of sensitivity and 2. a cochlear impairment reflects both a loss of sensitivity and of the compressive nonlinearity on the basilar membrane. Recently, there has been an increase in the number of psychoacoustical studies on hearing-impaired listeners with a majority of them directed toward revealing deficits in monaural processing. However, in most acoustic environments encountered in everyday life, there are multiple sounds originating from different sources, and hearing-impaired people often display less binaural advantage than do normally hearing persons. The results of the cu rrent study support the view of the lack of a simple relationship between monaural and binaural processing, which is often r eported in studies on hearing-impaired people. This is an important issue in the process of fitting hearing aids binaurally.

Loudness recruitment is an abnormally rapid growth of perceived loudness above the hearing threshold that slows to normal growth as the intensity of the signal increases. Recruitment is common in sensorineural hearing loss and in simulated hearing loss with noise masking. This study looked at possible differences in loudness recruitment with age, noise level, and frequency. Participants from two age groups were tested. Group A included participants aged 18 to 30 years and Group B included participants aged 50 to 75 years. Participants practiced the Alternate Binaural Loudness Balance (ABLB) test without noise present. They then repeated the tests with masking noise. Tests were completed with two different noise levels (50 dB SPL and 70 dB SPL), and two different test tone frequencies (1000 Hz and 2000 Hz). Participants identified loudness matching points to reference intensities of 20, 40, 60, and 80 dB HL. Participants completed 3 trials at each intensity level. Difference scores of the intensity of the loudness matching point minus the intensity of the reference tone were computed and analyzed statistically. An analysis of variance (ANOVA) for repeated measures fails to show significance for between-subjects effect for age, within subject effect for frequency, and trial. An ANOVA for repeated measures shows significant within subject effect for noise and for intensity. The 70 dB SPL noise level shows greater difference scores and a steeper loudness matching function slope than the 50 dB SPL noise level. The greater difference scores and steeper slope are expected due to the higher hearing threshold created with the higher noise level. As the intensity level increases, the difference score decreases. The decrease in difference scores with increasing intensity levels shows the presence of loudness recruitment. The results of this study suggest the use of masking noise in order to measure recruitment is an acceptable simulation. Age alone does not account for changes in loudness recruitment. Therefore, recruitment measurement with noise masking may be a potential marker of early auditory dysfunction.

Otoacoustic emissions (OAEs) are generated in the cochlea in response to sound and are used clinically to separate ears with normal hearing from sensorineural hearing loss (SNHL). OAEs were elicited at ambient pressure by clicks (CEOAE) and wideband chirps (TEOAE) sweeping from low-to-high frequency with a sweep rate of either 187.6 Hz/ms (short chirps) or 58.2 Hz/ms (long chirps) and a bandwidth extending to 8 kHz. Chirps were presented at the same sound exposure level (SEL) as clicks, or + 6 dB relative to clicks. A total of 288 OAE waveforms were averaged for short chirps in ~1 minute compared to 120 waveforms for long chirps. Compared to clicks, the chirp has a lower crest factor, which allows it to be presented at an overall higher SEL without distortion. OAEs were elicited in 79 adults with normal hearing and 51 adults with mild-to-moderate SNHL. One-sixth octave OAE signal-to-noise ratios from 0.7 to 8.0 kHz were compared across stimulus types and conditions. The area under the receiver operating curve (AUC) was used to assess the accuracy of detecting SNHL. Average AUCs across 1/6th octave frequencies ranged from 0.90 to 0.89 for TEOAEs and were 0.87 for the CEOAE suggesting excellent test performance.

Purpose: Listening effort has traditionally been measured using subjective rating scales and behavioral measures. Recent physiological measures of listening effort have utilized pupil dilation. Using a combination of physiological and subjective measures of listening effort, this study aimed to identify differences in listening effort during 2 auditory tasks: sentence recognition and word recognition. Method: Pupil dilation and subjective ratings of listening effort were obtained for auditory tasks utilizing AzBio sentences recognition and Northwestern University Auditory Test No. 6 words recognition, across 3 listening situations: in quiet, at +6 dB signal-to-noise ratio, and at 0 dB signal-to-noise ratio. Task accuracy was recorded for each of the 6 conditions, as well as peak pupil dilation and a subjective rating of listening effort. Results: A significant impact of listening situation (quiet vs. noise) and task type (sentence recognition vs. word recognition) on both physiological and subjective measures was found. There was a significant interaction between listening situation and task type, suggesting that contextual cues may only be beneficial when audibility is uncompromised. The current study found no correlation between the physiological and subjective measures, possibly suggesting that these measures analyze different aspects of cognitive effort in a listening task.

Age affects hearing and cognitive abilities. Older people, with and without hearing impairment (HI), exhibit difficulties in hearing speech in noise. Elderly individuals show greater difficulty in segregating target speech from distracting background noise, especially if the noise is competing speech with meaningful contents, so called informational maskers. Working memory capacity (WMC) has proven to be a crucial factor in comprehending speech in noise, especially for people with hearing loss. In auditory scenes where speech is disrupted by competing speech, high WMC has proven to facilitate the ability to segregate target speech and inhibit responses to irrelevant information. People with low WMC are more prone to be disrupted by competing speech and exhibit more difficulties in hearing target speech in complex listening environments. Furthermore, elderly individuals with a HI experience more difficulties in switching attention between wanted and irrelevant stimuli, and they employ more resources and time to attend to the stimuli than do normally - hearing (NH) younger adults. This thesis investigated the importance of inhibitory control and WMC for speech recognition in noise, and perceived listening effort. Four studies were conducted. In the first study, the aim was to develop a test of inhibitory control for verbal content, and to investigate the relation between inhibitory control and WMC, and how these two abilities related to speech recognition in noise, in young normally – hearing (YNH) individuals. In the second study we aimed to investigate the same relationship as in the first study to further strengthen the validity of the inhibitory test developed, as well as the importance of lexical access. It was also an aim to investigate the influence of age and hearing status on lexical access and WMC, and their respective roles for speech recognition in noise in both YNH and elderly HI (EHI) individuals. Study one and two showed that, for YNH, inhibitory control was related to speech recognition in noise, indicating that inhibitory control can help to predict speech recognition in noise performance. The relationship between WMC and speech recognition in noise in YNH shifted in the studies, suggesting that this relationship is multifaceted and varying. Lexical access was of little importance for YNH, although for EHI individuals, both WMC and lexical access was of importance for speech recognition in noise, suggesting that different cognitive abilities were of importance for the YNH and EHI individuals Study three investigated the relationship between inhibitory control, WMC, speech recognition in noise, and perceived listening effort, in YNH and elderly, for their age, NH, individuals (ENH). In study four the same relationships as in study three were investigated, albeit in EHI individuals. Two speech materials with different characteristics, masked with four background noises were used. The results in study three showed that less favourable SNRs were needed for informational maskers than for maskers without semantic content. ENH individuals were more susceptible to informational maskers than YNH individuals. In contrast, in study four, more favourable SNRs were needed for informational maskers. In both studies, results showed that speech recognition in noise performance differed depending on the characteristics of the speech material. The studies showed that high WMC, compared to low WMC, was beneficial for speech recognition in noise, especially for informational maskers, and resulted in lower ratings of perceived effort. Varying results were found in study three and four regarding perceived effort and inhibitory control. In study three good inhibitory control was associated with lower effort rating, while in study four, individuals with a HI and good inhibitory control rated effort as higher. The results suggest that hearing status, age, and cognitive abilities, contribute to the differences in performance between YNH, ENH, and EHI individuals in speech – recognition – in – noise - and cognitive tasks. This thesis has, for the first time, demonstrated that a measure of inhibitory control of verbal content, is related to speech recognition in noise performance in YNH, ENH and EHI individuals. Results presented in this thesis also show that both WMC and inhibitory control are related to an individuals’ perception of how effortful a listening task is. It also adds to the literature that WMC is related to speech recognition in noise performance for ENH and EHI individuals, but that this relationship is not as robust in YNH individuals. / Ålder påverkar hörseln och de kognitiva förmågorna. Äldre personer, med och utan hörselnedsättning, uppvisar ofta svårigheter att höra tal i miljöer med bakgrundsljud. De uppvisar större svårigheter att urskilja en måltalare, speciellt om det omgivande ljudet består av annat tal med meningsfullt innehåll, så kallad informationsmaskering. Arbetsminne har visat sig vara en viktig faktor för att förstå tal – i – brus, framför allt för personer med hörselnedsättning. I ljudmiljöer där tal störs av andra talkällor är hög arbetsminneskapacitet av vikt för att understödja förmågan att urskilja måltalaren från de störande talkällorna genom att underlätta inhiberingen av irrelevant information. Individer med lägre arbetsminneskapacitet är mer benägna att störas av andra talkällor, och har svårare att uppfatta måltalaren i komplexa lyssningssituationer. Vidare upplever äldre personer med hörselnedsättning att det är svårare att skifta uppmärksamheten mellan relevant och irrelevant stimuli, och de använder mer resurser och tid till omgivande stimuli än, ex. yngre individer med normal hörsel. I den här avhandlingen undersöktes vikten av inhibitionskontroll och arbetsminne vid taluppfattning i brus och upplevelsen av lyssningsansträngning. Fyra studier genomfördes. Syftet med första studien var att utveckla ett test för verbal inhibitionskontroll, och att undersöka relationen mellan inhibitionskontroll, arbetsminneskapacitet, och deras koppling till taluppfattning i brus hos yngre normalhörande personer. I studie två undersöktes ovanstående relationer för att vidare styrka validiteten för testet av inhibitionskontroll, samt vikten av lexikal åtkomst. Vidare syfte var att undersöka ålderns och hörselns inverkan på lexikal åtkomst och arbetsminneskapacitet, och deras respektive roller för taluppfattning i brus hos både yngre normalhörande och äldre hörselnedsatta personer. Studie ett och två visade att inhibitionskontroll var relaterad till taluppfattning i brus för yngre normalhörande personer, vilket indikerar att inhibitionskontroll kan användas för att underlätta att förutsäga förmågan att uppfatta tal – i – brus. Relationen mellan arbetsminneskapacitet och taluppfattning i brus hos yngre normalhörande var inte solid, vilket tyder på att relationen är mångsidig och skiftande. Lexikal åtkomst var av mindre betydelse för yngre normalhörande personer, ehuru hos äldre hörselskadade personer var både arbetsminneskapacitet och lexikal åtkomst viktigt för taluppfattning i brus. Detta tyder på att olika kognitiva förmågor var betydelsefulla för taluppfattningen i brus för yngre normalhörande och äldre hörselskadade personer. Studie tre undersökte relationen mellan inhibitionskontroll, arbetsminneskapacitet, taluppfattning i brus, och upplevd lyssningsansträngning hos yngre och äldre, för sin ålder, normalhörande personer. Två talmaterial med olika karakteristika användes och maskerades med fyra olika bakgrundsbrus. Resultatet visade att mindre gynnsamma signal – brus - förhållanden uppnåddes när informationsmaskering användes jämfört med brus utan semantiskt innehåll. Äldre normalhörande personer var mer mottagliga för informationsmaskering än yngre normalhörande personer. Hög arbetsminneskapacitet och god inhibitionskontroll var förmånliga för taluppfattning i brus, och resulterade i mindre upplevd lyssningsansträngning, jämfört med personer med lägre arbetsminneskapacitet och sämre inhibitionskontroll. Resultaten talar för att åldersrelaterade tillbakagångar i hörförmåga och, vissa, kognitiva förmågor, bidrar till skillnaderna i prestation mellan yngre och äldre normalhörande personer när det gäller förmågan att uppfatta tal - i - brus. Studie fyra undersökte samma relationer som i studie tre, ehuru hos äldre personer med mild – måttlig sensorineural hörselnedsättning. Resultaten visade att förmågan att uppfatta tal - i - brus varierade beroende på talmaterialets karakteristika, samt vilket bakgrundsbrus som användes. Hög arbetsminneskapacitet och god inhibitionskontroll var fördelaktiga för taluppfattningen, i synnerhet när informationsmaskering användes. Personer med högt arbetsminne upplevde mindre lyssningsansträngning, medan god inhibitionskontroll associerades med högre upplevd lyssningsansträngning. I föreliggande avhandling har det, för första gången, påvisats att verbal inhibitionskontroll relaterar till förmågan att uppfatta tal – i – brus hos yngre och äldre normalhörande, och äldre personer med hörselnedsättning. Resultaten som presenterats i avhandlingen visar att både arbetsminneskapacitet och inhibitionskontroll är associerade med en individs upplevelse av hur ansträngande en lyssningssituation är. Avhandlingen stödjer även tidigare forskning som visar på att arbetsminneskapaciteten är relaterad till förmågan att uppfatta tal – i – brus hos äldre  normalhörande, och äldre hörselskadade personer, men att denna relation inte är lika solid för yngre normalhörande personer.

The purpose of this study was to examine temporal resolution in normal-hearing preschool children. Word recognition was evaluated in quiet and in spectrally identical continuous and interrupted noise at signal-to-noise ratios (S/Ns) of 10, 0, and −10dB−10dB−10dB. Sixteen children 4to5years4to5years4to5yearsof age and eight adults participated. Performance decreased with decreasing S/N. At poorer S/Ns, participants demonstrated superior performance or a release from masking in the interrupted noise. Adults performed better than children, yet the release from masking was equivalent. Collectively these findings are consistent with the notion that preschool children suffer from poorer processing efficiency rather than temporal resolution per se.

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